1. Field of the Invention
The present invention relates to a quality control method for transmitting information which have various traffic conditions, such as voice, moving pictures and data by an ATM (Asynchronous Transfer Mode) switching.
2. Related Arts
The broadband ISDN (Integrated Services Digital Network) has been studied and developed as a next-generation communication network by which to provide standardized communication services for various types of information, such as voice, moving pictures and data.
The ATM (Asynchronous Transfer Mode) technique is a technique whereby, regardless of the communication speeds required for information, such as voice, moving pictures and data, all of which have a different traffic condition requirements, all the information is converted into a packet, called a cell, having a fixed length, and the cell is transmitted at high speed.
According to the ATM switching, the quality of the communication service must be adjusted in accordance with the traffic condition requirements for the information to be transferred.
Recently, advisory organizations, such as the ITU-T (International Telecommunication Union, Telecommunication Standardization Sector) and the ATM Forum, have formulated declaration procedures which enable an ATM network user to select one of various quality control types to declare in consonance with the operating condition or the use for which the network is applied.
To provide quality control for ATM switching, the above advisory organizations have defined the following five basic functions and their relevant control principles.
(1) Call Admission Control (CAC)
This control function is used to ascertain whether a setup connection can be used for a communication having a predetermined quality which was previously declared by a call signal.
(2) Usage Parameter Control (UPC)
This control function is used for monitoring the number of cells (the traffic) transmitted to an ATM switch, in accordance with the transfer capacity which was originally declared using a call signal.
(3) Shaping Control
This control function is used for the storing cells in a buffer memory when the traffic exceeds the maximum transfer capacity, and for restricting and averaging the transfer capacity.
(4) Priority Control
This control function is used for determining whether or not ATM cells are classified as priority cells, and for abandoning ATM cells that are not classified as priority cells at first.
(5) Congestion Control
This control function is used to reduce traffic congestion. Specifically, the acceptance of a call is halted, or an ATM cell is transmitted by being rerouted around a connection at which a congested condition exists.
In the ATM switch, the degree to which the functions are implemented and the capabilities (accuracy) of the functions greatly depend on the performance of a controller, which is hardware which is employed to achieve the above functions. Basic control of these functions is provided by software.
FIG. 18 is a flowchart showing the conventional quality control provided for an ATM switch. When a call signal requesting that a connection be set up is transmitted by a subscriber""s terminal to the ATM switch, the ATM switch analyzes accompanying declared information, which is included in the call signal, concerning quality control provisions (step S1). Then, the ATM switch selects a capability identifier QCP, which corresponds to a specific quality control factor requested in the declared information, for the controller which provides the quality control function for a connection in the ATM switch (step S2). The QCP is a capability identifier for identifying the quality control capability of the controller, and, as an example, has twelve levels (QCP 1 to QCP 12). When, at step S3, it is determined that consistency that quality control according to the capability identifier QCP can be provided or not, the controller (hardware) provides the quality control for a connection in accordance with the determined capability identifier QCP (step S4). As is described above, conventionally, a one-to-one correspondence is employed when setting the capability identifier QCP for a requested quality.
Assumed is a case wherein in this situation the contents of an advisory from one of the above advisory organizations, or the contents of an operation initiated by a user are changed, and a communication service which ensures a higher quality is requested, or a case wherein a future communication service that ensures better quality control may become available as a result of an improvement in the performance of the hardware. In such a case, since, as described above, for conventional software control a one-to-one correspondence is employed when setting the capability identifier QCP for the requested quality, a new ATM switch must be introduced, or an ATM network configuration must be rearranged (e.g., a countermeasure is employed whereby an ATM switch which can provide a high level of quality control is installed at the entrance of a conventional network) in order to achieve a higher quality communication service.
However, the introduction of an new ATM switch or the rearrangement of a network increases the cost of the ATM switch or the running costs for the network, so that a great load will be imposed on the operator of an ATM network and the expansion property of the ATM network will be deteriorated, and accordingly, the services provided to network users may be degraded. Therefore, for ATM switching the quality control for a conventional ATM switch has a poor expansion property.
It is, therefore, one objective of the present invention to provide an ATM switch having an expansion property which can cope with a conventional high quality control operation, and a quality control method for an ATM connection.
To achieve the above objective, according to one aspect of the present invention, it is provided an ATM switch comprising:
a switch unit for routing an ATM cell input from an ATM connection at an input site to the ATM connection at an output site;
a controller for controlling the quality of the ATM connection; and
a memory for storing a quality control identifier for linking declared information concerning the quality of the ATM connection, which is included in a call signal requesting the setup of the ATM connection, with a capability identifier for identifying the capability of the controller,
wherein the controller controls the quality of the ATM connection based on the capability corresponding to the capability identifier designated based on the quality control identifier obtained from the declared information.
With this arrangement, the quality control identifier for linking the declared information, which is included in a call signal, with the capability identifier, which identifies the capability of the controller for controlling the quality of an ATM connection, is introduced. If the quality requested in the declared information is changed due to a change in an advisory promulgated by an advisory organization, a different capability identifier can be assigned by changing or adding to the setup of the quality control identifier in accordance with the updated quality. Therefore, the quality control provided for the declared information can be easily changed to another type of quality control, and the expansion property of the ATM switch can be enhanced.
Furthermore, to achieve the above objective, according to another aspect of the present invention, it is provided a quality control method for controlling quality of an ATM connection comprising the steps of:
obtaining a quality control identifier from a declared information which is concerning the quality of the ATM connection and included in a call signal requesting the setup of the ATM connection and, the quality control identifier is for linking the declared information with a capability identifier for identifying the capability of a controller which controls the quality of the ATM connection;
designating the capability identifier based on obtained quality control identifier; and
controlling the quality of the ATM connection based on a capability corresponding to the designated capability identifier.
Other features and advantages of the present invention will become readily apparent from the following description when taken in conjunction with the accompanying drawings.